1. Field of the Invention
This invention relates to a planar light source apparatus suitable for use for illuminating, for example, a liquid crystal display panel, a display apparatus which incorporates a planar light source apparatus, and a planar illumination method applied to a planar light source apparatus.
2. Description of the Related Art
A planar light source apparatus for use as a backlight for a liquid crystal panel which is used in a television receiver or a like apparatus which includes a screen of a comparatively large size typically has such a configuration as shown in FIGS. 20 and 21. It is to be noted that FIG. 21 is a sectional view taken along line II-II of FIG. 20. Referring to FIGS. 20 and 21, the planar light source apparatus shown is of the type called direct type wherein it is disposed directly on the rear face of a display panel. In particular, a plurality of lamps 11 are disposed uniformly in a case formed from a reflective plate 10. The front face of the reflective plate 10 is painted in white so that light from the lamps 11 is reflected efficiently. For the lamps 11, for example, a CCFL tube (Cold Cathode Fluorescent Lamp) is used.
A diffusion plate 20 is disposed on the reflective plate 10 on which the lamps 11 are disposed such that light incident directly to the rear face of the diffusion plate 20 from the lamps 11 side, or light reflected by the reflective plate 10 and incident to the diffusion plate 20, is radiated from the front face of the diffusion plate 20. The rear face of the liquid crystal display panel is illuminated with the light radiated from the surface of the diffusion plate 20. The diffusion plate 20 is formed by mixing light dispersing material in a transparent resin plate or by adhering a sheet having a light diffusing action to the front face of the diffusion plate 20 so that the brightness on the front face of the diffusion plate 20 may be uniformized. To control the light emitting state of a planar light source apparatus so as to obtain uniform brightness is very significant in order to uniformize the luminance of the display screen.
An example of a backlight apparatus of the type described is disclosed in Japanese Patent Laid-Open No. Hei 8-221013.